Reactions that involve oxidoreductases activated by the coenzyme nicotinamide adenine dinucleotide to synthesize compounds of interest are widely used in industrial processes. Many of these compounds of interest are optically active compounds which are mainly produced as precursors of medicaments and agricultural chemicals (Non Patent Literatures 1 and 2). The redox reactions involving oxidoreductases are accompanied with either the conversion of NAD(P)+ (oxidized coenzyme) into NAD(P)H (reduced coenzyme) or the reverse conversion of NAD(P)H into NAD(P)+. Therefore, these redox reactions require a stoichiometric amount of NAD(P)+ or NAD(P)H. In industrial processes, it is preferable to avoid the use of a stoichiometric amount of such an expensive coenzyme. In this context, a technique that can reduce the amount of the expensive coenzyme has been used in industrial fields, in which the redox reaction is coupled with the conversion of the coenzyme formed as a result of the redox reaction into the form reusable for the reaction (oxidized form or reduced form) (Non Patent Literatures 2 and 3).
NAD(P)H oxidases are one of oxidoreductases that can be used for the conversion of NAD(P)H into NAD(P)+. Oxidation reactions of alcohols, amino acids, and the like which are catalyzed by nicotinamide coenzyme-dependent oxidoreductases utilize NAD(P)+ and produce NAD(P)H. NAD(P)H oxidases, which catalyze the conversion of NAD(P)H into NAD(P)+, can be involved in the oxidation of alcohols, amino acids, and the like, as an enzyme for regenerating NAD(P)+ (as a second enzyme system) (Patent Literatures 1 to 3 and Non Patent Literatures 3 and 4).
Well-known NAD(P)H oxidases used for industrial purposes are ones that produce a by-product such as hydrogen peroxide (H2O2) or water (H2O) as a result of reduction of molecular oxygen which occurs simultaneously with the oxidation of NAD(P)H to NAD(P)+ (Non Patent Literatures 3 and 4). Water-forming NAD(P)H oxidases are suitable for the NAD(P)+ regeneration system since they irreversibly catalyze the production of NAD(P)+ from NAD(P)H. H2O2-forming NAD(P)H oxidases are not easily used for enzyme-involved chemical reaction processes because produced H2O2 is toxic to enzymes. Therefore, ones that produce only water as a reaction product in addition to NAD(P)+ are preferred for industrial purposes.
Examples of known water-forming NAD(P)H oxidases include NADH oxidase derived from Lactobacillus brevis, NADH/NADPH (both can be substrates) oxidase derived from Lactobacillus sanfranciscensis, NADH oxidase derived from Pyrococcus furiosus, and NADH oxidase derived from Borrelia burgdorferi (Non Patent Literatures 4 to 6). Methods for synthesizing an optically active compound (optical resolution) have been proposed which utilize such a water-forming NAD(P)H oxidase as an NAD(P)+ regeneration system (Patent Literature 1 and Non Patent Literatures 5 to 8).
Water-forming NADH oxidases derived from bacteria of Streptococcus, in particular Streptococcus mutans, are also known (Patent Literature 2 and Non Patent Literatures 9 to 11). It has already been verified that these enzymes can be used as second enzyme systems for regenerating NAD(P)+ in oxidation reactions of alcohols, amino acids, and the like which are catalyzed by nicotinamide coenzyme-dependent oxidoreductases (Patent Literatures 3 and 4). These enzymes are characteristically known to efficiently catalyze the regeneration of NAD+ in the absence of enzyme stabilizers such as reductants (Patent Literature 2). This is a superior characteristic in terms of industrial usability, compared with other NAD(P)H oxidases such as NADH oxidase derived from Lactobacillus brevis which require an additive such as DTT (dithiothreitol) (Non Patent Literature 5).